diff --git a/manifest.yaml b/manifest.yaml
index a723ab8..5e3750d 100644
--- a/manifest.yaml
+++ b/manifest.yaml
@@ -7,8 +7,8 @@ dublin_core:
     description: ""
     format: text/usfm
     identifier: ulb
-    issued: 2020-05-05
-    modified: 2020-05-05
+    issued: '2020-05-05'
+    modified: '2020-05-05'
     language:
         direction: ltr
         identifier: ru